The present disclosure relates to a recording apparatus using an MOPA (Master Oscillator Power Amplifier) for combining a mode-locked oscillation laser and an optical amplifier as a light source for recording.
A laser beam of high peak power, particularly, an ultra-short pulse beam is very effective to realize a nonlinear multi-photon absorption process.
It is expected to be applied to three-dimensional optical recording, ultrafine machining, non-destructive bioimaging, or the like which uses the absorption process.
For example, a method in which a transparent bulk material having a non-liner effect is irradiated with a laser beam of high output to thereby realize multilayer recording has been reported (see, ISOM2009 Digest Th-l-01, 2009, Seiji Kobayashi, Kimihiro Saito, Takashi Iwamura, Hisayuki Yamatsu, Toshihiro Horigome, Mitsuaki Oyamada, Kunihiko Hayashi, Daisuke Ueda, Norihiro Tanabe, and Hirotaka Miyamoto).
In this method, in comparison with the stacked disk in the related art, an inexpensive high-capacity recording medium may be realized.
Further, as the light source for emitting the laser beam of high output, a mode-locked titanium sapphire laser is used. In an example of ISOM2009 Digest Th-l-01, 2009, Seiji Kobayashi, Kimihiro Saito, Takashi Iwamura, Hisayuki Yamatsu, Toshihiro Horigome, Mitsuaki Oyamada, Kunihiko Hayashi, Daisuke Ueda, Norihiro Tanabe, and Hirotaka Miyamoto, emitted light of 810 nm of the titanium sapphire laser is converted into a wavelength of 405 nm by a SHG (Second Harmonic Generator), so that the converted wavelength is used as a light source which is advantageous to high-density recording.
In the case of the above described large and expensive solid-state laser, it is limited to applications to experiments executed in the laboratory (for example, see Corporation Spectra-Physics, [online], [Aug. 6, 2010 Search] Internet i_Series_Data_Sheet.pdf>.
Therefore, many researchers have attempted to develop a more compact and stable pulse light source based on a semiconductor for the purpose of practical use.
Similar to the above described method, in optical recording of the next generation, a blue-violet laser light source that is advantageous to the high-density recording of all semiconductors is strongly desired.
For example, it has been reported that a gain-switching laser realizes a peak power of 55 W when repeatedly performed at 1 MHz by strong excitation driving (see, Appl. Phys. Lett. 96, 051102 —2010, _M. Kuramoto, T. Oki, T. Sugahara, S. Kono, M. Ikeda, and H. Yokoyama).
However, in response to market demand for a high data transfer rate, a higher repetition frequency is necessary even in the light source for data recording.
Recently, in the blue laser light source that is advantageous for high-density recording, a light source of 100 W at a repetition frequency of 1 GHz has been reported (for example, see, APPLIED PHYSICS LETTERS 97, 021101 —2010, Rintaro Koda, Tomoyuki Oki, Takao Miyajima, Hideki Watanabe, Masaru Kuramoto, Masao Ikeda, and Hiroyuki Yokoyama).
The light source includes a semiconductor mode-locked laser and a semiconductor optical amplifier in a configuration called an MOPA (Master Oscillator Power Amplifier).
In a recording reproduction apparatus, recording data is obtained such that a recording address is applied for each recording unit in advance, and data is recorded in a corresponding position based on a wobble signal in which address information is embedded on an optical recording medium in advance. Thus, it is possible to reproduce target desired data by accessing a beam using the address information at the time of reproduction.
In an optical disc for recording, for example, a DVD or a Blu-ray disc (registered trademark), the optical recording medium is irradiated with a laser pulse in which a data clock is generated using a fundamental wave of the wobble signal in which the address information is embedded, and a modulation of the recording data is applied by being synchronized with the data clock.
Even in a case of using an MPOA light source in recording, for modulation of the recording data and an oscillation pulse of the laser it is necessary to perform recording while being subjected to synchronization.